A carbon fiber reinforced composite material comprising a carbon fiber and a matrix resin has excellent lightweight performance and dynamic characteristics, thus is widely used in aerospace applications, general industrial applications, including sports uses.
In sports uses, a carbon fiber reinforced composite material is often formed into a tubular carbon fiber reinforced composite material, and is used for a golf club shaft, a fishing rod, rackets of tennis and badminton, and the like. These applications are fields in which weight reduction is particularly required, and a method for increasing material strength is adopted as an example of weight reducing method.
In a carbon fiber reinforced composite material, a tubular carbon fiber reinforced composite material strength is increased by properly applying a carbon fiber having high strength or high elastic modulus. Patent Document 1 suggests tubular carbon fiber reinforced composite material having high torsional strength, by using a carbon fiber showing high strand tensile elastic modulus. However, in recent years, as the level of required characteristics to a carbon fiber reinforced composite material is increased, the material strength achievable only by improving performance of carbon fiber is being insufficient.
An epoxy resin is suitably used as a matrix resin of a carbon fiber reinforced composite material, in aspects of its excellent mechanical characteristics, good adhesion to a carbon fiber, and the like. Patent Document 2 suggests a tubular carbon fiber reinforced composite material having excellent cylinder bending strength and impact resistance, using a bisphenol F epoxy resin and an amine epoxy resin. Also, Patent Document 3 suggests a method for increasing a three-point bending strength of tubular carbon fiber reinforced composite material, by using an epoxy resin cured product cured at a specific degree of crosslinking.
A technology for increasing shear strength between a carbon fiber and a matrix resin is also disclosed. Patent Document 4 discloses a method for increasing crushing strength and impact resistance of tubular carbon fiber reinforced composite material, by increasing in-plane shear strength.